base-dns.cpp

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/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
#include "base-dns.hpp"

#include <sys/types.h>
#include <netinet/in.h>
#include <resolv.h>
#include <arpa/nameser.h>

#ifdef __APPLE__
#include <arpa/nameser_compat.h>
#endif

namespace ndn {
namespace tools {
namespace autoconfig {

union BaseDns::QueryAnswer
{
  HEADER header;
  uint8_t buf[NS_PACKETSZ];
};

BaseDns::BaseDns(Face& face, KeyChain& keyChain, const NextStageCallback& nextStageOnFailure)
  : Base(face, keyChain, nextStageOnFailure)
{
}

std::string
BaseDns::querySrvRr(const std::string& fqdn)
{
  std::string srvDomain = "_ndn._udp." + fqdn;
  std::cerr << "Sending DNS query for SRV record for " << srvDomain << std::endl;

  res_init();

  _res.retrans = 1;
  _res.retry = 2;
  _res.ndots = 10;

  QueryAnswer queryAnswer;
  int answerSize = res_query(srvDomain.c_str(),
                             ns_c_in,
                             ns_t_srv,
                             queryAnswer.buf,
                             sizeof(queryAnswer));
  if (answerSize == 0) {
    BOOST_THROW_EXCEPTION(Error("No DNS SRV records found for " + srvDomain));
  }
  return parseSrvRr(queryAnswer, answerSize);
}

std::string
BaseDns::querySrvRrSearch()
{
  std::cerr << "Sending DNS query for SRV record for _ndn._udp" << std::endl;

  QueryAnswer queryAnswer;

  res_init();

  _res.retrans = 1;
  _res.retry = 2;
  _res.ndots = 10;

  int answerSize = res_search("_ndn._udp",
                              ns_c_in,
                              ns_t_srv,
                              queryAnswer.buf,
                              sizeof(queryAnswer));

  if (answerSize == 0) {
    BOOST_THROW_EXCEPTION(Error("No DNS SRV records found for _ndn._udp"));
  }

  return parseSrvRr(queryAnswer, answerSize);
}

std::string
BaseDns::parseSrvRr(const QueryAnswer& queryAnswer, int answerSize)
{
  // The references of the next classes are:
  // http://www.diablotin.com/librairie/networking/dnsbind/ch14_02.htm

  struct rechdr
  {
    uint16_t type;
    uint16_t iclass;
    uint32_t ttl;
    uint16_t length;
  };

  struct srv_t
  {
    uint16_t priority;
    uint16_t weight;
    uint16_t port;
    uint8_t* target;
  };

  if (ntohs(queryAnswer.header.ancount) == 0) {
    BOOST_THROW_EXCEPTION(Error("SRV record cannot be parsed"));
  }

  const uint8_t* blob = queryAnswer.buf + NS_HFIXEDSZ;

  blob += dn_skipname(blob, queryAnswer.buf + answerSize) + NS_QFIXEDSZ;

  char srvName[NS_MAXDNAME];
  int serverNameSize = dn_expand(queryAnswer.buf,               // message pointer
                                 queryAnswer.buf + answerSize,  // end of message
                                 blob,                          // compressed server name
                                 srvName,                       // expanded server name
                                 NS_MAXDNAME);
  if (serverNameSize <= 0) {
    BOOST_THROW_EXCEPTION(Error("SRV record cannot be parsed (error decoding domain name)"));
  }

  const srv_t* server = reinterpret_cast<const srv_t*>(&blob[sizeof(rechdr)]);
  uint16_t convertedPort = be16toh(server->port);

  blob += serverNameSize + NS_HFIXEDSZ + NS_QFIXEDSZ;

  char hostName[NS_MAXDNAME];
  int hostNameSize = dn_expand(queryAnswer.buf,               // message pointer
                               queryAnswer.buf + answerSize,  // end of message
                               blob,                          // compressed host name
                               hostName,                      // expanded host name
                               NS_MAXDNAME);
  if (hostNameSize <= 0) {
    BOOST_THROW_EXCEPTION(Error("SRV record cannot be parsed (error decoding host name)"));
  }

  std::string uri = "udp://";
  uri.append(hostName);
  uri.append(":");
  uri.append(to_string(convertedPort));

  return uri;
}

} // namespace autoconfig
} // namespace tools
} // namespace ndn